A Pox on Your Flowers

A mysterious strain of downy mildew has been killing one of the home gardener’s favorite annual flowers, Impatiens walleriana, up and down the East and West Coasts, in the Midwest, Texas and Ontario.

“We saw it here in 2011 in the fall, and it was really dramatic,” said Margery Daughtrey, a plant pathologist at the Cornell University extension center in Riverhead, N.Y. “Gorgeous plants, flowering two feet tall, and then the flowers start disappearing and leaves drop and stems fall over and then the stems disappear.”

Since then, it has only worsened. Lois Carswell, the co-chair of the Brooklyn Botanic Garden plant sale, which has been held in early spring for the last 60 years, said it has always done a brisk business in impatiens. But last year, the garden’s growers, which supply more than 20,000 plants for the sale, were seeing so many diseased plants in greenhouses and gardens that they decided not to offer Impatiens walleriana or any of its hybrids at this year’s sale later this month.

Impatiens is an overused plant I love to hate, so I am shedding crocodile tears. All those red-and-white, pink-and-purple flowers planted like petticoats under the trees — as if trees needed skirts. Maybe nature is doing us a favor by forcing those addicted to the plant to find an alternative.

Still, annual bedding plants are a $2 billion industry in the United States, and the colorful Impatiens walleriana has long been one of the best sellers. For years, it was sold by the millions by growers that buy seed from Ball Horticultural Company, Syngenta Seeds and others. And as recently as 2009, it reaped $174 million wholesale annually, according to the Agriculture Department. But now, the endangered pinup girl is having a rocky time in the marketplace. Some growers are still pumping it out, but many have stopped cold.

Walter Gravagna, an owner of Van de Wetering Greenhouses in Jamesport, N.Y., which produces 300 million plugs, or seedlings, of annuals a year, said his production is down by 20 percent. “We supply wholesalers from Michigan to Maryland and up to Maine, and 40 percent of that used to be impatiens,” he said. But “with downy mildew really hitting the East Coast, from the mid-Atlantic to Maine, that supply has gone down considerably.”

Home Depot is still selling the flats, but is training its staff to spot the disease and is educating customers about the risk involved if they insist on the one and only, said Stephen Holmes, a spokesman at the company’s headquarters in Atlanta. And “we’ll have less supply east of the Mississippi,” he said, where the flow of plants has been reduced by 25 to 40 percent.

The disease is a mold (Plasmopara obducens) that thrives in cool, damp conditions and first appears as a white, downy coating of spores on the undersides of leaves, so it’s easy to miss. By the time gardeners notice the flowers drooping, it’s too late to do anything.

So far, it has swept through 33 states and the District of Columbia, and has been confirmed in Ontario, with possible outbreaks in British Columbia and Quebec. It showed up in England in 2003, and spread so quickly through greenhouses and gardens that Britain’s Department for the Environment, Food and Rural Affairs placed a quarantine on the movement of diseased plants, Ms. Daughtrey said, “banning their sale, requiring disposal, that kind of thing.”

She continued: “In 2004, we saw a little bit of it in New York in greenhouses, and Tennessee and California. But it didn’t amount to much.”

Growers destroyed the infected plant material, stepped up their fungicide regimens, and the disease disappeared. Now and then, a sample would find its way into her lab at the Long Island Horticultural Research and Extension Center, but it didn’t seem to be cause for concern, because the disease only attacked Impatiens walleriana, and although it had been in North America since 1800, it hadn’t spread.

Then one morning in 2011, when Ms. Daughtrey stopped by her local bakery, she looked down at the cheery flower beds and thought they looked a little funny. She turned over a few leaves. “Lo and behold,” she said, “it was downy mildew.”

When she started looking around, she found it nearly everywhere else around town. “I documented it,” she said. “But no samples were brought to me, nobody ever asked about it. It was really strange.”

Few people called plant hot lines or their suppliers, either. That may be because when plants collapse, home gardeners often assume it is due to some insect or animal, or their own doing, as did Tom Hall, the music director of the Baltimore Choral Arts Society.

“When they started wilting last summer,” he said, “I thought maybe a cat had come in and peed on them or something. But by the end of summer, all of them were in bad shape, and now I know why.”

Every spring for the last 26 years, Mr. Hall has gotten a hundred or so plants at the farmers’ market for about $10 a flat, and planted them under the tree in front of the house he bought 27 years ago.

What kind of tree?

“I don’t know,” Mr. Hall said. “It loses its leaves in the fall.”

Who cares about the tree anyway? It’s the color of those velvety blooms nodding their pretty heads together that counts.

“Some summers they would get two-and-a-half feet tall, this eruption of color,” he said. “It seemed to bring people joy, the flowers were so festive and bright.”

Now he doesn’t know what he will do.

The industry is touting New Guinea impatiens as an alternative, because it is not susceptible to downy mildew. But Mr. Hall hasn’t had much luck with it. “I tried New Guinea impatiens on my back deck and I lost most of them,” he said. “Either they burned out in too much sun, or I watered them too much or not enough. And they were a lot more expensive.”

He is still grieving like someone who has lost a lover. “I suppose I’m set in my ways, but I’ve never found anything else,” he said. “And I want to stay away from things I have to deadhead.”

Impatiens was such a cinch: he just watered every morning and fertilized with Miracle-Gro once a week. (Poor tree, getting all that nitrogen and water, like a diet of candy for an elephant.)

But even if Mr. Hall can find Impatiens walleriana this spring — and many garden centers and box stores will still carry it — horticulturists warn not to plant it in the same place it has been blooming for years.

This mildew has two types of spores: short-lived spores, which form the white down on the undersides of the leaves and disperse when splashed with water or blown by the wind, and resting spores, produced inside infected stems and released into the soil, where they can live through the winter and infect new plants.

And since people love to plant a sea of impatiens, the disease can easily spread down the street or be carried for miles by wind. That’s why it is important to dig up all the diseased plants and bag them for trash removal. Don’t compost them, because the spores can spread.

Some growers and retailers have stopped selling impatiens altogether. Bianca Sullivan, owner of Colorful Gardens in Calverton, N.Y., sees it as a moral issue and has replaced all her Impatiens walleriana, including the double impatiens and exotic varieties that made up 15 percent of her sales, with New Guinea impatiens. “Why set the consumer up to fail?” she said.

Valley View Farms, a popular garden center near Baltimore, is not selling impatiens, either, said Ruth Engel, who tends annuals there. “Impatiens is our number one selling plant, and it’s sad not to be offering it,” she said. “But if people continue to plant it, the disease will continue, and no one has a real cure for it.”

And Ball Horticultural Company’s growers and their retailers are offering fewer impatiens this year, in areas hard-hit by downy mildew. As Colleen Warfield, the company’s corporate plant pathologist, said, “Certainly in New York and Cape Cod, we don’t expect people to be using as many impatiens.”

But other parts of the country, especially dry or mountainous regions, haven’t seen any evidence of the disease, she added. And “most people get a full season of color out of their impatiens, even if it gets infected by late in the season.”

Still, for those like Mr. Hall, who watched his beloved flowers collapse, it’s best to find another plant, said Margaret Falk, associate vice president for landscape, gardens and living collections at the New York Botanical Garden.

“We’re not going to have healthy impatiens in the East for a while,” she said. That bed of impatiens might look good now because it’s been sprayed with fungicides, but by June or so, it could well collapse.

So find yourself a new love, Mr. Hall, and soldier on.

Alternative Sources of Color

Die-hard impatiens lovers who must have a sweep of nonstop color from April through the first frost might want to try torenia, or wishbone flower instead, so-called for the little wishbone that hovers inside its throat. It thrives in partial shade, takes heat and humidity and comes in many colors, including sapphire blue.

Wax begonias are another option: their flowers look like impatiens from a distance, but they have more-interesting leaves, more colors and they don’t guzzle as much water.

So are the various renditions of Begonia boliviensis, a trailing species that runs the spectrum from demure little yellow flowers to deep red blooms that dangle like sexy earrings from sword-shaped leaves.

Coleus, once a ho-hum burgundy foliage plant, now dresses in lime-green, vermilion, orange and velvety deep chocolate. Its leaves can be heart-shaped or indented, like little hands. And I’m a sucker for blue-green hostas under trees.

But these are safe choices. Consider the collapse of your favorite annual as an invitation to adventure. Native perennials, for example, might cost a bit more, but they don’t have to be planted each year and they attract pollinators.

Corydalis lutea thrives in dry shade, has soft green fingerlike leaves and racemes of yellow spurred flowers that bloom from spring to fall. Add a little wild bleeding heart, whose teardrop pink flowers hover over gray-green fringed leaves. Both are beautiful with ferns (some, like the ostrich fern, have edible fiddleheads) and Heuchera americana, whose patterned leaves come in many colors, including yellow.

Both the New York Botanical Garden and the Brooklyn Botanic Garden will soon open new native flora gardens where visitors can observe these plants in lovely combinations. Many other alternatives to impatiens can be found at the Brooklyn Botanic Garden’s Plant Sale, May 1 and 2 (with a members-only preview sale on April 30; bbg.org), and at the sale held by the Manhattan Chapter of the North American Rock Garden Society on April 28 (mcnargs.org).